Hitherto, various types of epoxy resins have been widely made and used on a commercial basis.
Epoxy resins which have been widely used in industries include so-called epi-bis type epoxy resins produced by reacting bisphenol A with epichrolhydrine.
These resins have advantages, e.g., various products can be obtained, from a state of liquid to solid, and they can be cured at room temperatures with polyamines because the reactivity of the epoxy resins is high.
However, the cured products thereof are defective in that the outdoor durability is poor, the electric properties such as anti-tracking property, etc., are poor, and the heat distortion temperature is low, although they do have desirable characteristics of good water resistance and strength.
Recently, particularly epoxy resins prepared by reacting phenolic resin or novolak resin with epichrolhydrine have been used as resins for encapsulating VLSI (very large scale integrated circuit), etc., but chlorine contained in the resins, typically in an amount of several hundred parts per million, causes the problem of a deterioration of the electric properties of such electronic devices.
Epoxy resins having excellent electric properties and heat resistance, and which do not contain chlorine are known, such as certain alicyclic epoxy resins which are produced by an epoxidation reaction of a compound having a 5- or 6-membered cycloalkenyl structure.
The epoxy group in these resins is a so-called inner epoxy group, and curing is usually carried out with acid anhydride by heating.
However, since their reactivity is low, they cannot be cured with polyamines at room temperatures, and therefore, the use of the alicyclic epoxy resins has so far been technically restricted.
As alicyclic epoxy resins, those having a structure represented by formula (VII) or (VII) are presently used on a commercial basis. ##STR1##
(VII) is used as a heat resistible epoxy diluent, because of its very low viscosity.
However, it has the disadvantage of possessing high toxicity and causes the problem of poisoning upon contact with the skin of the human body.
(VIII) contains only a small amount of impurities and has a low color hue, and the cured products produced therewith have a high heat distortion temperature.
However, much epoxy resins suffer from the problem that they possess poor water resistance due to the presence of ester bonds.
In addition, because (VII) and (VIII) are epoxy resins having a low viscosity, it is impossible to apply molding systems for solid epoxy resins, such as transfer molding, etc., thereto.
From the above viewpoint, novel alicyclic epoxy resins which have oxycyclohexane units derived from 4-vinylcyclohexene-1-oxide were disclosed in Japanese Publication (Kokai) No. 166675/1985, corresponding to U.S. Pat. No. 4,565,859.
In addition, novel alicyclic epoxy resins which have oxynorbornane units derived from 4-vinylbicyclo[2.2.1]heptene-1-oxide in place of oxycyclohexane units were disclosed in Japanese Application (Priority) No. 215526/1987, etc., corresponding to U.S. Pat. No. 4,841,017.
Further, novel alicyclic epoxy resins, which have closslinked structures between the oxycyclohexane units, were disclosed in Japanese Application (Priority) No. 50361/1987, etc.
Nevertheless, the above epoxy resins do not have a completely sufficient water resistance and resistance to hydrolysis, because of the ether units and hydroxyl groups.
It is noted that the ether units are formed by the ring opening of the epoxy groups possessed by 4-vinylcyclohexene-1-oxide or 4-vinylbicyclo[2.2.1]heptene-1-oxide, and that the hydroxyl groups are derived from an initiating agent for a ring-opening reaction.
In addition, not only the overcoming of the above described problems, but also the number of methods or objects involving the use of epoxy resins have grown, and so have the desired characteristics of such epoxy resins; for example, demands for epoxy resins having excellent water resistance and excellent ductility have increased.